John Gills Exposition of the Bible Commentary - Genesis 21:10
Wherefore she said unto Abraham, cast out this bondwoman and her son ,.... Hagar, Sarah's handmaid and bondservant, and her son Ishmael; by this it appears that Hagar was concerned in this affair, and set her son on to mock Isaac, at least she encouraged him in it, buoying: him up with his being the firstborn, and having a right to the inheritance; wherefore Sarah saw plainly that there would be no peace nor comfort for her and her son, unless Hagar and her son were turned out of doors, for... read more
Matthew Henry's Complete Commentary - Genesis 21:9-13
The casting out of Ishmael is here considered of, and resolved on. I. Ishmael himself gave the occasion by some affronts he gave to Isaac his little brother, some think on the day that Abraham made the feast for joy that Isaac was safely weaned, which the Jews say was not till he was three years old, others say five. Sarah herself was an eye-witness of the abuse: she saw the son of the Egyptian mocking (Gen. 21:9), mocking Isaac, no doubt, for it is said, with reference to this (Gal. 4:29),... read more